Well we didn't attack Iraq directly because of the 9/11 attacks.

#1 there was Saddam in charge
#2 possibility of WMD's/harboring terrorist (proved false...way to go UK intelligence!)

My main reasoning behind it is this: Iraq in the Middle East in a very strategic location for military bases. Between the more democratic (Egypt, Israel) and the more hardcore islamic (Syria, Iran, Saudi Arabia, UAE, etc) countries thus it provides the perfect place to try to put bases and troops to prevent anything happening involving any of those countries. Although the counter point to that is the fact that terrorism and guerilla warfare is being used more and more and hell no one wants to go toe to toe with the US Armed Forces, it's a fact, not even China with it's billions of people want us in a real war.